This invention relates to aqueous compositions of surfactant mixtures with hydrophobically-modified polymers. In particular, the invention concerns the use of selected surfactant mixtures with hydrophobically-modified polymeric rheology modifiers (thickeners) to provide enhanced thickening efficiency otherwise not available with conventional surfactant/thickener combinations. Compositions of the present invention are useful as thickening agents in a variety of formulations, such as decorative and protective coatings, paper coatings, cosmetics and personal care items, detergents, pharmaceuticals, adhesives and sealants, agricultural formulations, petroleum drilling fluids and cleaners.
Rheology modifiers, or thickeners, have several roles in aqueous systems. They increase viscosity and maintain viscosity at required levels under specified processing conditions and end use situations. In latex decorative coatings, for example, the thickener may provide improved stability, pigment suspension and application properties. In cosmetics and personal care items, the thickener improves body, smoothness and silkiness, making the product more aesthetically pleasing. In petroleum drilling fluids, the thickener improves the suspension of the cuttings, increasing the efficiency with which they can be removed.
Many rheology modifiers, both natural and synthetic, are known. Natural rheology modifiers include, for example, casein, alginates, gum tragacanth, and modified cellulose, including methyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose and carbomethoxy cellulose. These natural products vary in their thickening efficiency and generally provide poor flow and leveling properties; they are also subject to microbial attack and require the additional presence of antimicrobial agents. Synthetic rheology modifiers include various acrylic polymers and maleic anhydride copolymers. Some of these are found to be pH dependent, others are hydrolytically unstable, some require large amounts of thickener to effectively increase viscosity, and others are sensitive to various components normally found in aqueous coatings.
A variety of methods have been used to improve the thickening properties of aqueous solutions. For example, the effect of added surfactant on aqueous phase viscosity in the presence of hydrophobically-modified urethane-ethoxylate polymers is disclosed by M. Hulden in Colloids and Surfaces A: Physicochemical and Engineering Aspects, 82, pp 263-277 (1996). Similarly, surfactant/thickener interactions are disclosed in "A Study of the Interaction of Hydrophobically-Modified Polyols with Surfactants" by C. E. Jones, Proceedings of the 4th World Surfactants Congress, CESIO, Barcelona, 2, pp 439-450 (1996) and in "Tailoring the Properties of Polymeric Rheology Modifiers to the Characteristics and Requirements of Personal Care Formulations" by P. Reeve, Proceedings of International Federation of Society of Cosmetic Chemists, IFSCC, Budapest, April 1997. Another approach for improving the thickening properties of aqueous solutions using macromonomer-modified polymers as co-thickeners with surfactants is disclosed in U.S. Pat. No. 5,292,843.
The problem addressed by the present invention is to overcome the deficiencies of the prior methods used to increase the viscosity of aqueous systems by providing a thickener composition that can be used at low use levels and in the presence of a wide range of formulation additives (for example, surfactants, salts and pigments) without suffering from compatibility problems.